Methods of manufacturing mercury sorbents and removing mercuryfrom a gas stream

ABSTRACT

Sorbents for removal of mercury and other pollutants from gas streams, such as a flue gas stream from coal-fired utility plants, and methods for their manufacture and use are disclosed. The methods include injecting a sorbent consisting essentially of recovered and separated fluid cracking catalyst particles into a flue gas stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §120 toU.S. application Ser. No. 11/763,691, filed Jun. 15, 2007, which claimsthe benefit of priority under 35 U.S.C. §119(e) to U.S. ProvisionalApplication Ser. No. 60/805,188, filed Jun. 19, 2006, which areincorporated herein by reference.

FIELD OF THE INVENTION

Embodiments of the invention relate to sorbents for the removal ofpollutants such as mercury from gas streams, methods for manufacturingsorbents and the use of sorbents in pollution control.

BACKGROUND

Emission of pollutants, for example, mercury, from sources such ascoal-fired and oil-fired boilers has become a major environmentalconcern. Mercury (Hg) is a potent neurotoxin that can affect humanhealth at very low concentrations. The largest source of mercuryemission in the United States is coal-fired electric power plants.Coal-fired power plants account for between one-third and one-half oftotal mercury emissions in the United States. Mercury is foundpredominantly in the vapor-phase in coal-fired boiler flue gas. Mercurycan also be bound to fly ash in the flue gas.

On Dec. 15, 2003, the Environmental Protection Agency (EPA) proposedstandards for emissions of mercury from coal-fired electric powerplants, under the authority of Sections 111 and 112 of the Clean AirAct. In their first phase, the standards could require a 29% reductionin emissions by 2008 or 2010, depending on the regulatory option chosenby the government. In addition to EPA's regulatory effort, in the UnitedStates Congress, numerous bills recently have been introduced toregulate these emissions. These regulatory and legislative initiativesto reduce mercury emissions indicate a need for improvements in mercuryemission technology.

There are three basic forms of Hg in the flue gas from a coal-firedelectric utility boiler: elemental Hg (referred to herein by the symbolHg0); compounds of oxidized Hg (referred to herein the symbol Hg2+); andparticle-bound mercury. Oxidized mercury compounds in the flue gas froma coal-fired electric utility boiler may include mercury chloride(HgCl₂), mercury oxide (Hg0), and mercury sulfate (HgSO₄). Oxidizedmercury compounds are sometimes referred to collectively as ionicmercury. This is because, while oxidized mercury compounds may not existas mercuric ions in the boiler flue gas, these compounds are measured asionic mercury by the speciation test method used to measure oxidized Hg.The term speciation is used to denote the relative amounts of thesethree forms of Hg in the flue gas of the boiler. High temperaturesgenerated by combustion in a coal boiler furnace vaporize Hg in thecoal. The resulting gaseous Hg0 exiting the furnace combustion zone canundergo subsequent oxidation in the flue gas by several mechanisms. Thepredominant oxidized Hg species in boiler flue gases is believed to beHgCl₂. Other possible oxidized species may include HgO, HgSO₄, andmercuric nitrate monohydrate (Hg(NO₃)₂.H₂O).

Gaseous Hg (both Hg0 and Hg2+) can be adsorbed by the solid particles inboiler flue gas. Adsorption refers to the phenomenon where a vapormolecule in a gas stream contacts the surface of a solid particle and isheld there by attractive forces between the vapor molecule and thesolid. Solid particles are present in all coal-fired electric utilityboiler flue gas as a result of the ash that is generated duringcombustion of the coal. Ash that exits the furnace with the flue gas iscalled fly ash. Other types of solid particles, called sorbents, may beintroduced into the flue gas stream (e.g., lime, powdered activatedcarbon) for pollutant emission control. Both types of particles mayadsorb gaseous Hg in the boiler flue gas.

Sorbents used to capture mercury and other pollutants in flue gas arecharacterized by their physical and chemical properties. The most commonphysical characterization is surface area. The interior of certainsorbent particles are highly porous. The surface area of sorbents may bedetermined using the Brunauer, Emmett, and Teller (BET) method of N₂adsorption. Surface areas of currently used sorbents range from 5 m²/gfor Ca-based sorbents to over 2000 m²/g for highly porous activatedcarbons. EPA Report, Control of Mercury Emissions From Coal-FiredElectric Utility Boilers, Interim Report, EPA-600/R-01-109, April 2002.For most sorbents, mercury capture often increases with increasingsurface area of the sorbent.

Mercury and other pollutants can be captured and removed from a flue gasstream by injection of a sorbent into the exhaust stream with subsequentcollection in a particulate matter control device such as anelectrostatic precipitator or a fabric filter. Adsorptive capture of Hgfrom flue gas is a complex process that involves many variables. Thesevariables include the temperature and composition of the flue gas, theconcentration of Hg in the exhaust stream, and the physical and chemicalcharacteristics of the sorbent. Of the known Hg sorbents, activatedcarbon and calcium-based sorbents have been the most actively studied.

Currently, the most commonly used method for mercury emission reductionis the injection of powdered activated carbon into the flue stream ofcoal-fired and oil-fired plants. Currently, there is no availablecontrol method that efficiently collects all mercury species present inthe flue gas stream. Coal-fired combustion flue gas streams are ofparticular concern because their composition includes trace amounts ofacid gases, including SO₂ and SO₃, NO and NO₂, and HCl. These acid gaseshave been shown to degrade the performance of activated carbon. Thoughpowdered activated carbon is effective to capture oxidized mercuryspecies such as Hg+2, powdered activated carbon (PAC) is not aseffective for elemental mercury which constitutes a major Hg species influe gas, especially for subbituminous coals and lignite. There havebeen efforts to enhance the Hg0 trapping efficiency of PAC byincorporating bromine species. This, however, not only introducessignificantly higher cost, but a disadvantage to this approach is thatbromine itself is a potential environmental hazard. Furthermore, thepresence of PAC hinders the use of the fly ash in the cement industryand other applications due to its color and other properties.

As noted above, alternatives to PAC sorbents have been utilized toreduce mercury emissions from coal-fired boilers. Examples of sorbentsthat have been used for mercury removal include those disclosed inUnited States Patent Application Publication No. 2003/0103882 and inU.S. Pat. No. 6,719,828. In United States Patent Application PublicationNo. 2003/0103882, calcium carbonate and kaolin from paper mill wastesludge were calcined and used for Hg removal at high temperatures above170° C., preferably 500° C.

In addition, sorbents having metal sulfides on the sorbent particlesurfaces and/or between layers of layered sorbents such as clayparticles have been provided. Examples of such sorbents are described inU.S. Pat. No. 6,719,828 and pending, commonly assigned U.S. patentapplication Ser. No. 11/290,631 filed Nov. 30, 2005. In U.S. patentapplication Ser. No. 11/290,631, particles such as bentonite, kaolin,metakaolin, fly ash, zeolite, silica, alumina and common dirt havingcopper sulfide dispersed on the surface were shown to be effectivemercury sorbents.

While sorbents modified with metal sulfides have showed promisingresults, the modification of the particles with a metal sulfide requiresadditional manufacturing steps and reagents. There is an ongoing need toprovide improved pollution control sorbents and methods for theirmanufacture, particularly sorbents that are in abundant supply andrequire minimal processing.

DETAILED DESCRIPTION

Aspects of the invention include methods and systems for removal ofheavy metals and other pollutants from gas streams. In particular, themethods and systems are useful for, but not limited to, the removal ofmercury from flue gas streams generated by the combustion of coal. Oneaspect of the present invention relates to a sorbent comprising fluidcracking catalyst particles (“FCC particles”). The FCC particles may beobtained from the end stage or intermediate stage of an FCC particlemanufacturing process, or alternatively, they may be generated during afluid catalytic cracking process that uses FCC particles and generatesFCC fine particles. In particular embodiments, the methods and systemsutilize fluid cracking catalyst fine particles, which will beinterchangeably referred to as “FCC fines” or “FCC fine particles”. Thefluid cracking catalyst fine particles may be recovered and separatedfrom a fluid cracking catalyst manufacturing process or recovered andseparated from a fluid catalytic cracking process that uses FCCparticles and generates FCC fines. Another aspect of the inventionpertains to sorbents comprising intermediate FCC fines, which are fineparticles obtained from an intermediate step of a fluid crackingcatalyst particle manufacturing process. In specific embodiments,zeolite-containing FCC fines and intermediate FCC fines are provided assorbents for the removal of mercury from gas streams.

One or more embodiments of the invention are directed to methods ofremoving mercury and other pollutants from a flue gas stream comprisinginjecting a sorbent consisting essentially of recovered and separatedfluid cracking catalyst (FCC) particles into the flue gas stream.

In another embodiment, a method of removing mercury and other pollutantsfrom a gas stream, for example, from the flue gases of coal-fired andoil-fired boilers, is provided comprising injecting a sorbent comprisingrecovered and separated fluid cracking catalyst particles into the fluegas stream. In certain embodiments, the particles are fine particles. Inone or more embodiments, the particles contain essentially no addedmetal sulfides on the surface of the particles.

According to one or more embodiments, the fine particles have an averageparticle diameter of less than about 40 microns, for example, an averageparticle diameter of between about 20 microns and 40 microns. In certainembodiments, the fine particles have an average particle diameter ofless than about 20 microns.

In one or more embodiments, the fluid cracking catalyst particlescontain at least one of zeolite, hydrous kaolin, metakaolin, sodiumsilicate, silica and alumina. The content of each component in FCCproducts can be present in an amount from zero to 100% by weight. Thezeolite content of the particles according to one or more embodiments isless than about 90% by weight. In other embodiments, the zeolite contentof the particles is less than about 50% by weight, and in yet anotherembodiment, the zeolite content is less than about 40% by weight. Thezeolite is a Y-type zeolite according to one or more embodiments.

In certain embodiments, the zeolite particles are obtained from anintermediate stage of a FCC particle manufacturing process. According toone or more embodiments, the FCC particles are obtained prior to ionexchange during the manufacturing process.

Another aspect of the invention pertains to a method of manufacturing amercury sorbent comprising recovering particles from a FCC particlemanufacturing process, and packaging the particles for shipment. In oneembodiment, the particles are recovered from an intermediate step of anFCC particle manufacturing process. In certain embodiments, FCCparticles are recovered prior to ion exchange. According to one or moreembodiments, the FCC particles include a zeolite, for example, a Y-typezeolite. Before describing several exemplary embodiments of theinvention, it is to be understood that the invention is not limited tothe details of construction or process steps set forth in the followingdescription. The invention is capable of other embodiments and of beingpracticed or being carried out in various ways.

Aspects of the invention provide improved sorbents, which may be used toremove mercury and other pollutants from the flue gases of coal-firedand oil-fired boilers, methods for manufacturing such sorbents, andsystems and methods utilizing these sorbents. In one or moreembodiments, the sorbents comprise FCC catalyst particles that do notcontain metal sulfides on the particle surface.

During the production of these FCC catalysts, an amount of fineparticles in the range of about 0 to 40 μm in excess of that requiredfor good fluidization in the refinery are often generated. Heretofore, asuitable use for these excess fine particles has not been found, and sothey are therefore land-filled, which incurs cost for the plants. Thedisposal of the FCC waste by-products, referred as FCC fines, has been along-standing concern for FCC manufacturing.

Thus, the use of FCC fines as a mercury removal injection sorbent notonly provides an economical sorbent for processes that require a largevolume of sorbent, but also helps solve the FCC waste disposal issue.Furthermore, since no additional raw materials or equipment is requiredto make the FCC fines sorbent, the use of FCC fines will result insignificantly reduced sorbent manufacturing costs. From the point ofview of environmental protection, this is an ideal case in which theland fill of FCC fines is eliminated, a sorbent is provided that removesmercury from flue gas streams, and the use of natural resources andenergy for making the sorbent is reduced.

The terms “fluid cracking catalyst fines” or “FCC fines” are used hereinto refer to fine solid particles obtained from a fluid cracking catalystmanufacturing process, such as described in, but not limited to U.S.Pat. Nos. 6,656,347 and 6,673,235, and to particles generated andseparated during a fluid catalytic cracking process that uses FCCparticles. For particles formed during a fluid catalytic crackingparticles manufacturing process, the particles may be separated duringone or more intermediate stages of the manufacturing process, or at anend stage. For example, the particles may be separated prior to ionexchange, and these particles may be referred to as “pre-ion exchange”particles. Alternatively, the particles may be separated after ionexchange, and these particles may be referred to as “ion exchangedparticles” or “post-ion exchange particles.” In another embodiment, theparticles may be separated either before calcination, and may bereferred to as “pre-calcination particles” or after calcination and maybe referred to as “post-calcination particles.” The terms “intermediatefluid cracking catalyst fines” or “intermediate FCC fines” refers toparticles obtained during an intermediate stage of a fluid crackingcatalyst powder manufacturing process. FCC catalysts containing about15% of 0-40 μm fines are used for petroleum refining via a fluidcracking catalysis process.

Intermediate FCC fines or excess FCC fines are generated in theprocesses described in U.S. Pat. Nos. 6,656,347 and 6,673,235 in twoprinciple ways. In the first route, pre-formed microspheres containing amixture of calcined kaolins are immersed in sodium silicate solution tocrystallize zeolite Y, and several percent of excess fines are generatedover and above the amount present in the original microspheres. Thefines can contain sodium form zeolite Y, gmelinite, and leached kaolinresidue. The excess material is separated by centrifuge, settling andfiltration, and then ordinarily discarded. The second route for finesformation is microsphere attrition during handling in the ion exchangeportion of the manufacturing processes. Ion exchange is done to replaceunwanted sodium with more desirable ions. Pneumatic transportation,rotary calcination and stirring lead to particle-particle andparticle-wall collisions and the formation of fines. Several percent ofexcess fines are generated over and above the amount present in therequired particle size distribution. The fines can contain ammonium/rareearth-form zeolite Y and gmelinite or their collapsed residues, andleached kaolin residue. These are also separated by centrifuge, settlingand filtration, and then ordinarily discarded. Waste fines from thevarious latter stages of the process are combined together into thissingle process stream.

In one or more embodiments the catalyst fines are waste materialobtained from a point in the catalyst manufacturing procedure afterreaction to form a zeolite intermediate. In other embodiments, FCC finesare obtained after ion exchange as, for example, waste material from adrying step or from a calcining step. In one or more embodiments, thefines or fine particles have an average particle size of less than about40 microns in diameter, for example, an average particle size of betweenabout 20 and 40 microns in diameter microns in diameter. In otherembodiments, the average particle size of the fine particles is lessthan about 20 microns in diameter.

In still other embodiments, FCC fines are obtained after the catalysthas been used in the catalytic cracking process in the oil refinery. Theused FCC catalyst from the refinery is commonly referred to as“equilibrium catalyst” or E-cat, and this catalyst is of a reducedsurface area and activity, and may contain contaminant metals suchnickel, vanadium, iron and copper, as well as incremental amounts ofsodium, calcium and carbon. Most of the existing equilibrium catalyst isof a larger particle size above 40 μm, typically about 80 μm, butequilibrium catalyst fines are also available. Some of the fines arenothing more than essentially fresh FCC catalyst with a particle sizeless than 40 μm, since the FCC hardware has limited success at retainingthese particles. The other portion of the equilibrium catalyst fines isof a lower surface area and activity, and these are formed byparticle-particle and particle-wall collisions during use which leads toparticle attrition and fines. The two types of fines form a mixture thatis not typically separated into its components. These fines are found inthe bottoms of the FCC main distillation column or in collection devicessuch as an electrostatic precipitator or a wet gas scrubber. A portionof the fines is also lost to the atmosphere. The effectiveness of thesematerials has not been measured but it is presently speculated thatthese may be useful as a mercury adsorbent.

FCC manufacturing processes are known, and examples of manufacturingprocesses for zeolite-containing FCC particles are described in thepatents cited above, as well as U.S. Pat. Nos. 3,663,165; 4,493,902 and4,699,893, which are incorporated herein by reference. In oneembodiment, as described in U.S. Pat. No. 3,663,165, preformedmicrospheres are obtained by calcining a spray dried slurry of hydrouskaolin clay at elevated temperature (e.g., 1800° F.) are suspended in anaqueous sodium hydroxide solution together with a small amount of finelydivided metakaolin (e.g., kaolin clay calcined at 1350° F.). Thesuspension is aged and then heated until crystalline sodium faujasiteappears in the microspheres and sodium silicate mother liquor is formed.The crystallized microspheres are ion-exchanged to produce a zeoliticcracking catalyst. Fines or fine particles can be obtained either priorto or after ion-exchange and used as a mercury sorbent as describedfurther below.

As noted above, additional examples of processes for manufacturing FCCcatalysts are described in commonly assigned U.S. Pat. Nos. 6,656,347and 6,673,235, the contents of each patent being incorporated herein byreference. In U.S. Pat. No. 6,673,235, an FCC catalyst is made frommicrospheres, which initially contain kaolin, binder, and a matrixderived from a dispersible boehmite alumina and an ultra fine hydrouskaolin having a particulate size such that 90 Wt % of the hydrous kaolinparticle are less than 2 microns, and which is pulverized and calcinedthrough the exotherm. The microsphere is subsequently converted usingstandard in-situ Y zeolite growing procedures to make a Y-containingcatalyst. Exchanges with ammonium and rare earth cations withappropriate calcinations provides an FCC catalyst that contains atransitional alumina obtained from the boehmite and a catalyst of aunique morphology to achieve effective conversion of hydrocarbon tocracked gasoline products with improved bottoms cracking under SCT FCCprocessing. Preparation of the Such a Fluid Cracking Catalyst, asdescribed in U.S. Pat. No. 6,673,235, may involve an initial step ofpreparing microspheres comprising hydrous kaolin and/or metakaolin, adispersible boehmite (Al₂O₃, H₂O), kaolin calcined through itscharacteristic exotherm and derived from ultra fine hydrous kaolin, anda binder. The microspheres are calcined to convert any hydrous kaolincomponent to metakaolin. The calcination process transforms thedispersible boehmite into a transitional alumina phase. The calcinedmicrospheres are reacted with an alkaline sodium silicate solution tocrystallize zeolite Y and ion-exchanged. The transitional alumina phasethat results from the dispersible boehmite during the preparativeprocedure and which forms the matrix of the final catalyst, passivatesthe Ni and V that are deposited on to the catalyst during the crackingprocess, especially during cracking of heavy residuum feeds. Thisresults in a substantial reduction in contaminant coke and hydrogenyields. Contaminant coke and hydrogen arise due to the presence of Niand V and reduction of these byproducts significantly improves FCCoperation.

In U.S. Pat. No. 6,656,347, novel zeolite microspheres are formed whichare macroporous, have sufficient levels of zeolite to be very active andare of a unique morphology to achieve effective conversion ofhydrocarbons to cracked gasoline products with improved bottoms crackingunder SCT FCC processing. The novel zeolite microspheres are produced bya modification of technology described in U.S. Pat. No. 4,493,902. Byusing non-zeolite, alumina-rich matrix of the catalyst derived from anultrafine hydrous kaolin source having a particulate size such that 90wt. % of the hydrous kaolin particles are less than 2 microns, and whichis pulverized and calcined through the exotherm, a macroporous zeolitemicrosphere is produced. Generally, the FCC catalyst matrix useful inthe '347 patent to achieve FCC catalyst macroporosity is derived fromalumina sources, such as kaolin calcined through the exotherm, that havea specified water pore volume.

It will be understood, of course, that the present invention should notbe limited to the above cited FCC manufacturing processes. Thetechniques for manufacturing FCC catalysts referred to above, are oftenreferred to in the art as in-situ techniques. Other techniques formanufacturing FCC catalysts may be utilized to provide sorbents used formercury capture. For example, zeolite-containing FCC catalysts may bemanufactured using a process in which the zeolitic component iscrystallized and then incorporated into microspheres in a separate step.This type of manufacturing process may be referred to as anincorporation process for manufacturing FCC particles.

In one or more embodiments, the FCC fines sorbent particles comprise amixture of zeolite, sodium silicates, metakaolin, silica, and alumina.In certain embodiments, the FCC particles are composed mainly of Yzeolite and minor components of sodium silicates, metakaolin, andadditives such as silica and alumina. Y-type zeolite FCC catalysts areproduced by growing a Y-type zeolite first from metakaolin and sodiumsilicate slurry, followed by rare earth ion-exchange, spraying andcalcination.

In initial experiments to determine the mercury absorption of zeoliteand FCC catalysts, these catalysts were tested for their ability toremove mercuric ions (Hg⁺²) from water. The Hg capture efficiency wassignificantly lower than standard activated carbon. Severalaluminosilicate minerals such as bentonite and fly ash were tested forremoving mercury in flues gas and found their activity was also too lowto be considered. When FCC fines with CuS on the surface of the fineswere tested, the sorbent activity was good and comparable to thosesupported on other minerals like bentonite. However, when FCC finesalone without any metal sulfide on the surface of the FCC fines wereinjected into a flue gas stream, both the ionic and elemental mercurycapture was acceptable. It is not presently understood whichcomponent(s) in the FCC fines are responsible for the high Hg activitysince pure Y-type zeolite or La-exchanged Y-type zeolite gave lowerHg-capture efficiency than the FCC fines. However, the ability to removeHg from flue gas by using FCC fines without additional trapping agents,such as metal sulfide, represents a breakthrough with many benefits asoutlined above.

Without intending to limit the invention in any manner, the presentinvention will be more fully described by the following examples.

EXAMPLES

Several samples were prepared in accordance with the methods formanufacturing sorbent substrates described above.

Comparative Example 1 FCC Fines Containing CuS

Initial experiments focused on mixing FCC fines with CuS in accordancewith methods described in U.S. patent application Ser. No. 11/290,631.Samples were made by grinding 2.90 g of CuSO₄.5H₂O and 0.97 g ofCuCl₂.2H₂O and separately drying and grinding a wet cake obtained from aFundabac® filter of an FCC manufacturing process.

The mixture of copper salts was added to 10.0 g of dried Y-zeolite, andthe mixture was thoroughly ground. To this mixture, 4.16 g of Na₂S.9H₂Owas added, and the mixture was ground thoroughly. The wet paste washeated in an oven at 105° C. overnight. The dried material was groundand passed though a 325 mesh sieve. This sample is labeled as SampleD-CuS.

Example 2 Preparation of FCC Fines

A wet cake of Y-type zeolite FCC fines prior to ion exchange wasobtained from a Fundabac® filter and was dried at 105° C. overnight.This sample contained sodium silicate mother liquor waste and had a highsodium content. A second wet cake was obtained after lanthanum ionexchange and was dried at 105° C. overnight. Each dried sample wasseparately passed through a 325 mesh sieve. The first sample obtainedprior to ion exchange was labeled sample A, and the second,ion-exchanged sample was labeled sample B. A third sample labeled CBV100was obtained from Zeolyst of Valley Forge, Pa. CBV100 is a 100% Yzeolite powder. This sample was labeled CBV100. A second sample ofCBV100 was ion exchanged with La, and this sample is labeled CBV100-La.The main physical and chemical properties of these materials are shownbelow.

TABLE 1 Physical Properties Surface Area (m²/g) N₂ Pore Volume N₂ PoreDiameter Particle Size (μM) Substrate N₂ ZSA Total (cc/g) (nm) D₅₀ D₉₀Sample A 241 273 0.23 3.3 11.9 33.5 Sample B 204 300 0.46 6.1 22.1 70.3CBV100 666 715 0.38 2.1 4.7 16.7 Main Chemical Composition (%) SiO₂Al₂O₃ Na₂O LaO Fe₂O₃ TiO₂ K₂O MgO + CaO Sample A 56.0 27.7 14.0 0.000.52 0.81 0.37 0.20 Sample B 60.9 26.7 6.5 2.94 0.90 0.96 0.12 0.14CBV100 65.3 21.6 12.6 0.00 0.03 0.01 0.01 0.20

Example 3 Initial Mercury Capture Efficiency Measurements

The mercury capture efficiency was measured by Western KentuckyUniversity (CISET) using an in-flight reactor. The flue gas was producedin a coal-fired pilot plant and duct-piped into the reactor. Mercuryspeciation and assay was conducted using CEM and Ontario-hydro methods.The sorbent residence time in the reactor is 1 second, sorbent injectionrate 4 lbs/MMCF, and flue gas temperature 150° C.

Mercury Capture Efficiency (%) is Defined as:

100×[Hg(inlet)−Hg(outlet)]/[Hg(inlet)]

Table II lists the mercury capture efficiency of a total six sorbentsamples for elemental mercury, Hg(0) and total mercury,Hg(T)=Hg(ionic)+Hg(0). For comparison, two reference materials are alsolisted: one is the current industry standard injection sorbent, Darco-LHbrominated activated carbon obtained from Norit, and the other is BN100,which is CuS/bentonite sorbent produced at Engelhard Elyria plantprepared in accordance with the methods disclosed in U.S. applicationSer. No. 11/291,091, filed on Nov. 30, 2005 (Now U.S. Publication No.2007/0122327) and entitled Methods of Manufacturing Bentonite PollutionControl Sorbent. This sample was labeled Sample C.

Hg (inlet), ng/Nm³ Efficiency, % Sample Hg (T) Hg (0) Hg (T) Hg (0)Darco-LH 6000 4780 42.6 68.0 Darco-LH (repeat 1) 8332 3930 46.2 73.6Darco-LH (repeat 2) 5460 1915 48.3 72.5 Sample C 7818 2063 48.7 66.2Sample D-CuS 5900 4700 42.0 37.7 Sample A 6120 4880 41.3 50.0 Sample A(repeat 1) 6028 2069 40.3 28.6 Sample A (repeat 2) 5745 2052 56.0 63.0Sample B 7979 3429 31.6 33.5 CBV100 6320 3576 33.0 17.2 CBV100-La 68645657 35.1 30.1Sample D-CuS, which was a zeolite having CuS on the surface of theparticles exhibited lower elemental mercury capture efficiency, but agood mercury capture efficiency that is comparable to those sorbentssupported on other carriers such as bentonite. However, compared withthe two reference materials of Darco-LH and BN100, FCC fines alonewithout added CuS (sample A) exhibited good Hg-capture efficiency forboth Hg(T) and Hg(0), though low value of Hg(0). Repeat 1 of sample Aexhibited lower mercury capture, but Repeat 2 was consistent with thefirst sample A and comparable to Darco-LH, an industry standard. Theion-exchanged FCC fines (sample B) exhibited a significantly lowerHg-capture efficiency than the samples that were obtained from theintermediate stage prior to ion exchange. Sample B also has lower sodiumand zeolite content (ion-exchange capacity) and large particle size. Totest if the differences in zeolite content and particle size contributedto the different performance, CBV100 was tested because it is a purezeolite and has much smaller particle size. The Hg-capture efficiency ofCBV100 was not better than the Sample C. As noted above, Sample C wasion-exchanged with rare earth (lanthanum) cations. To determine theeffect of rare earth ion exchange on mercury capture, we alsoion-exchanged CBV100 with lanthanum cations, washed and dried thesample. No significant difference was found between the CBV100 and itsLa-exchanged CBV100 sample.

Example 4 Mercury Leachability Test and Results of Na—Y AluminosilicateFines Adsorbent

A TCLP (Toxicity Characteristic Leaching Procedure) test was conductedin a fixed bed reactor on Samples A and B from the above Examples. Thesamples were tested as follows: 0.5 gram of each sample was mixed withglass beads. The mixed sample was then subjected to loading on the fixedbed. The experimental temperature of the fixed bed was set at 150° C.The Hg(0) stream with a flow rate of 0.80 L/min and concentration at 100ug/NM³ was delivered to pass through the fixed bed for sorbentbreakthrough tests. The PSA SCEM was used to monitor Hg(0) and alsoHg(2+) concentrations downstream of the fixed bed until breakthroughoccurred. There was no evidence that the Hg(0) stream changed itsspeciation after passing through the mixed samples in the fixed bed.Following the fixed bed tests, the mixed samples were analyzed via aleaching test. Samples were analyzed according to Method 1311 ToxicityCharacteristic Leaching Procedure (TCLP). The sample was dissolved in anappropriate extraction solution then agitated for 19 hours. The leachingsolution was analyzed by Leeman instrument for determination of mercuryconcentration.

The results show that leachable Hg is 0.03% for Sample A and 0.11% forSample B. With 0.03% Hg leachability, the Sample A is classified asnon-hazardous material. In other words, Sample A, a waste product fromzeolite manufacturing not only effectively captures mercury in the fluegas, but also safely retains Hg in the spent adsorbent.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit or scope of the invention. Forexample, while the sorbents disclosed herein are particularly useful forremoval of mercury from the flue gas of coal-fired boilers, the sorbentscan be used to remove heavy metals such as mercury from other gasstreams, including the flue gas of municipal waste combustors, medicalwaste incinerators, and other Hg-emission sources. Thus, it is intendedthat the present invention cover modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalents.

1. A method of removing mercury and other pollutants from a flue gasstream comprising injecting a sorbent consisting essentially ofrecovered and separated fluid cracking catalyst (FCC) particles into theflue gas stream.
 2. The method of claim 1, wherein the FCC particles arefine particles.
 3. The method of claim 2, wherein the FCC particlescontain essentially no added metal sulfides on the surface of theparticles.
 4. The method of claim 2, wherein the FCC particles have anaverage particle diameter of less than about 40 microns.
 5. The methodof claim 4, wherein the FCC particles have an average particle diameterin the range of about 20 microns to about 40 microns.
 6. The method ofclaim 4, wherein the FCC particles have an average particle diameter ofless than about 20 microns.
 7. The method of claim 1, wherein the FCCparticles contain at least one of zeolite, hydrous kaolin, metakaolin,sodium silicate, silica, and alumina.
 8. The method of claim 7, whereinthe content of each component is in the range from zero to 100% byweight.
 9. The method of claim 7, wherein the zeolite is a y-typezeolite.
 10. The method of claim 7, wherein the FCC particles areobtained from an intermediate stage of an FCC manufacturing process. 11.The method of claim 10, wherein the FCC particles are separated by oneor more of a centrifuge, settling and filtration.
 12. The method ofclaim 10, wherein the FCC particles are obtained prior to ion exchange.13. The method of claim 10, wherein the FCC particles are obtained afterion exchange.
 14. The method of claim 10, wherein the FCC particles areobtained prior to calcination.
 15. The method of claim 10, wherein theFCC particles are obtained after calcination.
 16. The method of claim 1,wherein the flue gas stream originates from a coal-fired boiler.
 17. Themethod of claim 1, wherein the flue gas stream originates from anoil-fired boiler.
 18. The method of claim 1, wherein the flue gas streamoriginates from municipal waste combustion.
 19. The method of claim 1,wherein the flue gas stream originates from a medical waste incinerator.